Provision of location information

ABSTRACT

A method of providing information regarding the location of a mobile user equipment ( 1 ) in a system wherein the location is determined based on information signalled from entities ( 10 ) of a positioning system and assistance data signalled from a station ( 5 ) of a communication system. In the method the likely location of the mobile user equipment relative to the station is first determined. Based on the determined likely location, an estimate of the delay in transmitting a signal from the station to the mobile user equipment is estimated. Assistance data is then signalled from the station to the mobile user equipment, said assistance data comprising information about the timing of the positioning system. A more accurate location determination is accomplished at the user equipment based on signals from the entities of the positioning system, the assistance data and said estimated delay.

FIELD OF THE INVENTION

The present invention relates to provision of information regardinglocation of a mobile user equipment, and in particular to compensationof inaccuracies in timing information used in determining the locationof a mobile user equipment such as a mobile station.

BACKGROUND OF THE INVENTION

In wireless communication systems such as those known as cellularcommunications systems a mobile user equipment such as a mobile stationcommunicates with other stations via a wireless interface. In a cellularsystem the mobile user equipment such as a portable handset or othermobile station is served by radio access entities referred to as cells,hence the name cellular system. In a cellular system, the cell isprovided by means of a base transceiver station (BTS). A base stationmay provide more than one cell and a cell may be provided by more thatone base station. E.g. the 3^(rd) generation telecommunicationsstandards may refer to the base station as node B. Regardless thestandard, the term base station will be used in this document toencompass any such element of an access entity which transmits to and/orreceives signals from a mobile user equipment or the like via an airinterface.

As the approximate size and the shape of the cell is known, it ispossible to associate the cell to a geographical area. The size andshape of the cells may vary from cell to cell. One or several cells mayalso be grouped together to form a service area (SA).

Examples of cellular communication standards, without limiting thisspecification to these, include the second generation (2G) GSM (GlobalSystem for Mobile communications) or various GSM based systems (such as2G GPRS: General Packet Radio Service), the AMPS (American Mobile PhoneSystem), the DAMPS (Digital AMPS) or 3^(rd) generation (3G) cellularsystem systems, such as the 3G GPRS and communication systems based onthe WCDMA (Wideband Code Division Multiple Access), for example the UMTS(Universal Mobile Telecommunications System), IMT 2000, i-Phone and soon.

The cellular network apparatus and/or the mobile station can be employedfor provision of location information of the mobile station and thus theuser thereof. More particularly, the cells or similar geographicallylimited service areas and associated controller nodes facilitate thecellular system to produce at least a rough location informationestimate concerning the current geographical location of a particularmobile station. If the location of the access entity is known, it ispossible to conclude at least roughly from this information thegeographical area in which the given mobile user equipment(communicating in said access entity) is likely to be at a given moment.A mobile user equipment may also be provided with appropriate equipmentto generate information on which the positioning of the mobile userequipment can be based on.

Use of satellite based positioning systems for positioning of mobilestations has also been proposed. A well established satellite basedpositioning system is the GPS (global positioning system). Anotherexample of the satellite based positioning system is the proposedGalileo™ location system. In the satellite based systems the positioninginformation is provided by means of computations that are based on thelocations of the satellites and the timing of the positioning system.The timing arrangement is such that each satellite is synchronised tothe one system time, or “universal time”. In the following the timing ofthe GPS system will be referred to as the ‘GPS time’.

In operation, each GPS satellite continuously transmits a bit streamcontaining the satellite identity, the GPS time and satellite trajectorymodels. The trajectory models may comprise e.g. an approximate long termmodel (almanac) and an accurate short term model (ephemeris). A GPSreceiver can then estimate its location in three dimensional space basedon the signals, typically from at least four different GPS satellites,the GPS time and other information such as the trajectory models.

A mobile station may be provided with a GPS receiver. The GPS receiveris adapted to search for the satellites, and he receive the GPS signalsfrom the found satellites. Location determinations may then be performedat the mobile station based on the information signal received from thesatellites.

A further development in the field of the GPS and the positioning ofmobile stations is the so called Assisted Global Positioning System(A-GPS). The basic idea of the A-GPS is that the performance of a GPSreceiver of a mobile station is enhanced by sending appropriateassistance data to the mobile station. Instead of sending such data fromthe satellites, the assistance data is transmitted via the air interfacebetween the mobile station and the cellular network.

Various information may be provided as the assistance data. One of thecomponents of the assistance data may be the GPS time. The GPS time canbe used in assisting the GPS receiver to find more easily signals fromGPS satellites. Further gain is obtained if the GPS time can bedelivered to the mobile station (and its GPS receiver) as accurately aspossible, as this will make the computation more accurate. Furthermore,less than four satellites may be enough for accurate positioning of themobile station. The A-GPS is supported by various telecommunicationstandards, such as the 2G GSM and 3G UMTS specifications.

One possibility to transfer the GPS time to the mobile station is tosend information about the correspondence of the GPS time relative to atiming used by the cellular system. That is, the mobile station isprovided with information by means of which the GPS time can be tied toa certain event in the cellular system. This timing will herein bereferred to as the cellular time.

The association of the GPS time and the cellular time is alreadysupported, for example, by the GSM standards. For example, GSMspecification No. 04.35 (version 8.1.0) describes broadcasting of GPSassistance data to user equipment. In chapter 4.2.1.6 a so called‘Reference Time Information Element’ is defined as an informationelement (IE) that specifies the relationship between the GPS time andair-interface timing of the BTS transmission in the serving cell. In GSMspecification No. 04.31 the corresponding point-to-point information isdefined as fields that specify the relationship between the GPS time andair-interface timing of the BTS transmission in a reference cell.

Thus in the assisted GPS mobile location method a way of provision ofthe assistance data is to transfer the GPS time to the mobile byexpressing the correspondence of the GPS time relative to a certainevent in the cellular system. It has been proposed that in the GSM andUMTS standards the event comprises the moment of transmission of acertain signal. That is, the GPS time is expressed as a transmissionmoment of a certain cellular signal.

However, the Inventor has found that a problem may arise since themobile user equipment can only detect the reception time. Since therewill be at least some distance between the mobile user equipment and thetransmitting base station, the moment of transmission will be differentfrom the moment of reception due to the propagation delay. The mobileuser equipment cannot relate the reception time to the transmission timeof the relevant cellular signal, and thus the propagation delay maycause substantial inaccuracy in the delivered GPS time.

Best improvement in the location determination accuracy is believed torequire transferring of the GPS time with an error that is less than 10micro seconds. However, for example, in the GSM one bit period is 3.69micro-seconds. This accuracy corresponds to 1.1 km in distance. Themaximum cell size can be 35 km in a typical GSM system. Extended cellradius may also be used, these providing as large radiuses as 70 km.Thus the maximum possible propagation delay can be 116 microseconds. Thedelay is ten times more than the 10 micro second requirement, and equalsabout 34.6 km in distance.

SUMMARY OF THE INVENTION

Embodiments of the present invention aim to address the problem in theaccuracy of the timing information that is used by a station such asmobile user equipment in application comprising location determinationsthat are based on timing information.

According to one aspect of the present invention, there is provided amethod of providing information regarding the location of a mobile userequipment in a system wherein the location is determined based oninformation signalled from entities of a positioning system andassistance data signalled from a station of a communication system,comprising:

-   -   determining the likely location of the mobile user equipment        relative to the station;    -   based on the determined likely location, determining an estimate        of the delay between transmission of a signal from the station        and reception of said signal at the mobile user equipment;    -   signalling assistance data from the station to the mobile user        equipment, said assistance data comprising information about the        timing of the positioning system; and    -   accomplishing a more accurate location determination at the user        equipment based on signals from the entities of the positioning        system, the assistance data and said estimated delay.

According to another aspect of the present invention there is provided asystem for determining the location of a mobile user equipment,comprising:

-   -   a positioning system comprising entities arranged to signal        information, the arrangement being such that the mobile user        equipment may receive and use the information from said entities        when determining its location;    -   a station of a communication system arranged for transmission of        information signals to the mobile user equipment;    -   location estimation means for provision of an estimate of the        likely location of the mobile user equipment relative the        station;    -   processor means for provision of an estimate of the delay        between transmission of an information signal from the station        and reception of said information signal at the mobile user        equipment based on said estimated location; and    -   location determination means for determining the location of the        mobile user equipment based on signals from the entities of the        position system, assistance data from the station, said        assistance data comprising information about the timing of the        positioning system and said estimate of the delay.

According to one aspect of the present invention, there is provided amobile user equipment, comprising:

-   -   a first receiver for receiving information signals from entities        of a positioning system for use in location determinations by        the mobile user equipment;    -   a second receiver for receiving signals from a station of a        communication system; and    -   location determination means for determining the location of the        mobile user equipment based on signals from the entities of the        position system, assistance data signal received from the        station, said assistance data comprising information about the        timing of the positioning system, and a computed difference        between the time of transmission of said assistance data signal        from the station and the time of reception of said assistance        data signal at the mobile user equipment, said difference being        computed based on an estimated likely location of the mobile        user equipment relative to the base station.

In a more specific form information about the estimated delay istransmitted from the station to the mobile user equipment. The estimateabout the delay may alternatively be determined at the mobile userequipment.

The entities of the positioning system may comprise at least onesatellite.

The delay estimate may be used to relate the timing of the positioningsystem with the time at which the mobile user equipment is likely toreceive a certain signals. The signal may contain said assistance data.Said delay estimate may be included in the assistance data.

The likely location of the user equipment may be estimated based oninformation about the mass center of the coverage area of the station.Average timing advance (TA) or round trip time (RTT) may also be used inestimation of said delay. The likely location may also be determinedbased on information of the average location of the mobile userequipment and/or based on at least one signal strength measurement.

The embodiments of the invention may enable more accurate transfer oftiming information assistance data than what was possible in the priorart. Accurate timing information may be provided for user equipment thatis located in a cell that is larger than what was appropriate in theprior art solutions. The embodiments are also believed to be easy toimplement, and can be applied in the already existing positioningsystems.

BRIEF DESCRIPTION OF DRAWINGS

For better understanding of the present invention, reference will now bemade by way of example to the accompanying drawings in which:

FIG. 1 shows one embodiment of the present invention;

FIG. 2 shows an example of the operation of operation in accordance withthe present invention; and

FIG. 3 is a flowchart illustrating the operation of one embodiment ofthe present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Reference is first made to FIG. 1 which shows an embodiment of thepresent invention. The mobile user equipment comprises a mobile station1 arranged for communication with a base transceiver station 5 of a cellof a cellular communication system. The communication is shown to occurvia antenna means 3 of the mobile station. It shall, however, beappreciated that the antenna means 3 do not form an essential element ofthe present invention and may comprise any appropriate means forreception and, if necessary, transmission of signals. For example,antenna means may be integrated with any of the components of the mobilestation 1, such as the cover or an internal component thereof.

The mobile station 1 also comprises a GPS receiver 2. GPS receivers assuch are known and will thus not be explained in any greater detail. Itis sufficient to note that the GPS receiver 2 is adapted to receivesignals from GPS satellites 10. The GPS receiver 2 may also provide themobile station 1 with other location information determinationfunctions. The receiver 2 may, in addition to simply receiving signalsfrom the satellites, determine the location of the mobile station 1based on the signals from the GPS satellites 10 and assistance data fromthe base station 5.

In a cellular system each of the cells can be controlled by anappropriate controller apparatus (not shown). For example, in a WCDMAradio access network the base station is connected to and controlled bya radio network controller (RNC). In the GSM radio network the basestation is typically connected to and controlled by a base stationcontroller (BSC) of a base station subsystem (BSS). The BSC/RNC may bethen connected to and controlled by a mobile switching center (MSC) orsimilar controller entity. Other controller nodes may also be provided,such as a serving GPRS support node (SGSN). The controllers of acellular network are typically interconnected and there may be one ormore gateway nodes connecting the cellular network e.g. to a publicswitched telephone network (PSTN) and other telecommunication networkssuch as to the Internet and/or other packet switched networks. Since theoperation of the various controllers is not essential for the operationof the present invention, it is not necessary to shows or describe thesein any greater detail herein.

Entities such as a location measurement unit (LMU) 6 and a servingmobile location center (SMLC) 8 may also be provided. The operation ofthese entities will be explained later.

In operation the timing of the satellite based positioning system i.e.the GPS time is sent to the mobile station 1 as the assistanceinformation from the cellular system, see FIG. 2. As shown in FIG. 3,instead of using a GPS time that is linked to the broadcast transmissiontime T_(t) of a certain cellular signal in the cell, the GPS time islinked to the timing of the cellular system based on an estimatedreception time T_(r) of the cellular signal at the mobile station.

In TDMA (time division multiple access) cellular systems, such as e.g.in the GSM, the mobile station knows the so called timing advance (TA)value if it has a two-way communication channel open to the network. TheTA represents the back-and-forth time delay between the mobile stationand the servicing base station. In normal operation the mobile stationuses the TA to adjust its transmission timings in order to ensure thatits transmissions arrive at the servicing base station at the allocatedtime slot. Thus a mobile station that has an active connection with thebase station may already be provided with an estimate of the about thetime delay. However, another estimate of the delay is required even insuch situation e.g. when the mobile station does not have an activeconnection (the mobile station is, for example, in idle state) or whenit is not provided with the TA value for any other reason.

The reception time T_(r) may be estimated based on information about thelikely position 11 of the mobile station within the cell. Since thespeed of travel of the cellular signal is known, the likely location ofthe mobile station makes it possible to compute an estimate for thedelay (or offset) between the moments of transmission from the basestation 5 and the reception at the mobile station.

The estimation of the delay may be accomplished in any appropriatelocation service entity such as the Serving Mobile Location Center(SMLC) 8 or in the location measurement unit (LMU) 6. The estimation mayalso be accomplished by any of the network controllers. For example, abase station controller (BSC) or radio network controller (RNC) may beused for the provision of the estimate. It shall also be appreciatedthat the SMLC may be provided in connection with a BSC.

The GPS time may be “corrected” by the MS. This requires that the mobilestation is provided with information based on which it may compensateany delay in the reception time. For example, the assistance datamessage may comprise an additional information element such as a datafield for the delay information.

The delay may also be compensated by the network. That is, the delay maybe taken into account before sending the assistance data to the mobilestation. A possibility is to “distort” the GPS timing so that the delayis compensated.

In a preferred form the most likely position of the user equipment isestimated e.g. by means of the serving mobile location center 8. Themost likely position can be, for example, estimated based on informationabout the mass center of the coverage area of the cell i.e. the areawhere the mobile station can receive signals from the base station. Themass center can be computed by means of the software of the SMLC.

Another possibility is to estimate the location based on informationabout the so called weighted mass center of the coverage area of thecell. The weight can be selected e.g. based on information aboutpopulation density, roads, traffic densities, geographical informationand so on.

Average Timing Advance (TA) value may also be determined for the cell.This may be done e.g. by the operation and maintenance system, or by abase station controller (BSC). This kind of functionality is alreadysupported by some communication systems. The average TA may then be usedto determine the most likely location of the mobile station.

In the 3G systems the Round Trip Time (RTT) can be used in similarmanner to estimate the propagation delay and to compensate the delay inthe specific mobile station.

Various other techniques may also be used to improve the accuracy of thelocation determination. For example, methods such as range difference(RD) measurements, observed time difference of arrival (OTDOA), andenhanced observed time difference of arrival (E-OTD), may be used forestimation of the likely position of the mobile station.

The network may also collect information about average location of usersin the cell based on performed normal location determinations. These mayhave been done e.g. for commercial applications, such as in response torequest by location service clients. Any appropriate location service(LCS) entity, such as the SMLC 8 may be adapted for this purpose.

In some applications the cell middle point may be used as the likelylocation. This may be used e.g. for small cells such cells as whereinthe radius is less than 6 km. The estimated GPS time can then be usedfor the whole coverage area of that cell. This is probably a viablesolution for mobile stations located inside a building or e.g. in adense city canyon environment.

In accordance with an embodiment wherein the base station broadcasts theassistance data the broadcast may include information regarding thedelay in various locations, e.g. in certain distances away from the basestation. That is, the broadcast assistance data may include variousdelay estimates for mobile stations that are located differentlyrelative to the base station. A possibility for implementing this isthat the mobile station utilises the signal strength information todetermine roughly its location relative to the base station. The mobilestation may then select the appropriate delay estimate parameter fromthe broadcast based on the estimated location. A mobile stationtypically measures signal strengths from more than one base station. Themobile station may thus also base the location estimate on more than onesignal strength measurement.

The delay information may be included in the transmission of theassistance data. The delay information may be included e.g. in anappropriate data frame of the assistance data.

It should be appreciated that whilst embodiments of the presentinvention have been described in relation to mobile stations such asmobile phones, embodiments of the present invention are applicable toany other suitable type of mobile user equipment. What is required isthat the use equipment is provided with means for receiving signals fromat least two systems that are provided with different time bases.

The embodiment of the present invention has been described in thecontext of a cellular system. This invention is also applicable to anypositioning system wherein information about the delay in transmissionof a timing is required.

The positioning system does not necessarily need to be a satellite basedsystem. It cam be any positioning system, such as a local land basedsystem.

The above described the delay caused by the distance between the basestation and the mobile station. Other factors may also be taken intoaccount. For example, the propagation delay estimate may take intoaccount any delaying effect of conditions such as reflections andnon-line-of-sight (NLOS). For example, if a cell covers an area withsubstantially large and/or tall buildings blocking the direct signalpath between the base station and the mobile station, the delay estimatemay be adjusted to take into account the slightly longer propagationtime of signals in such conditions.

The location information service network element such as the SMLC or agateway mobile location center (GMLC) may act as a gateway between thecommunication network and a client who has requested for the locationinformation. The geographical location of a mobile user equipment may beprovided for client entities who are entitled to obtain suchinformation. The clients may be internal or external to thecommunication system. The location information server responds to therequest by the client based on information received from one or more ofthe location determination entities of the communication system, saidinformation regarding the determined location of a target mobile userequipment. The clients may use the information about provided by thelocation information services of the communication system for variouspurposes. The use may be commercial such as advertising, looking forservices in a particular area and so on. The location information mayalso be used for by various emergency services. The use may also beprivate, such as the ‘find a friend service’.

It is also noted herein that while the above describes exemplifyingembodiments of the invention, there are several variations andmodifications which may be made to the disclosed solution withoutdeparting from the scope of the present invention as defined in theappended claims.

1. A method of providing information regarding the location of a mobileuser equipment in a system wherein the location is determined based oninformation signalled from entities of a positioning system andassistance data signalled from a station of a communication system,comprising: determining the likely location of the mobile user equipmentrelative to the station; based on the determined likely location,determining an estimate of the delay between transmission of a signalfrom the station and reception of said signal at the mobile userequipment; signalling assistance data from the station to the mobileuser equipment, said assistance data comprising information about thetiming of the positioning system; and accomplishing a more accuratelocation determination at the user equipment based on signals from theentities of the positioning system, the assistance data and saidestimated delay.
 2. A method as claimed in claim 1, wherein informationabout the estimated delay is transmitted from the station to the mobileuser equipment.
 3. A method as claimed in claim 1, wherein the estimateof the delay is determined at the mobile user equipment.
 4. A method asclaimed in claim 1, wherein the entities of the positioning systemcomprise at least one satellite.
 5. A method as claimed in claim 4,wherein the positioning system comprises the global positioning system(GPS).
 6. A method as claimed in claim 1, wherein the delay estimate isused to relate the timing of the positioning system with the time atwhich the mobile user equipment is likely to receive a certain signalfrom the communication system.
 7. A method as claimed in claim 1,wherein the delay estimate is used to relate the timing of thepositioning system with the time at which the mobile user equipment islikely to receive said assistance data signal.
 8. A method as claimed inclaim 1, wherein said delay estimate is included in the assistance data.9. A method as claimed in claim 1, wherein the likely location of theuser equipment is estimated based on information about the mass centerof the coverage area of the station.
 10. A method as claimed in claim 9,comprising use of information about a weighted mass centre.
 11. A methodas claimed in claim 1, wherein average timing advance (TA) or round triptime (RTT) is used in estimation of said delay in transmission ofsignals from the station to the mobile user equipment.
 12. A method asclaimed in claim 1, wherein the likely location is determined based oninformation of the average location of the mobile user equipment.
 13. Amethod as claimed in claim 1, wherein the likely location is determinedbased on at least one signal strength measurement.
 14. A method asclaimed in claim 1, comprising broadcasting in a cell informationregarding estimated delay in transmission of signals from the basestation of the cell to a mobile user equipment in a location within saidcell.
 15. A method as claimed in claim 1, wherein the estimated delay intransmission of the signal from the station to the mobile user equipmentis determined based on information of at least one further conditionregarding the radio propagation conditions of signals transmitted fromthe station to the mobile user equipment.
 16. A system for determiningthe location of a mobile user equipment, comprising: a positioningsystem comprising entities arranged to signal information, thearrangement being such that the mobile user equipment may receive anduse the information from said entities when determining its location; astation of a communication system arranged for transmission ofinformation signals to the mobile user equipment; location estimationmeans for provision of an estimate of the likely location of the mobileuser equipment relative the station; processor means for provision of anestimate of the delay between transmission of an information signal fromthe station and reception of said information signal at the mobile userequipment based on said estimated location; and location determinationmeans for determining the location of the mobile user equipment based onsignals from the entities of the position system, assistance data fromthe station, said assistance data comprising information about thetiming of the positioning system and said estimate of the delay.
 17. Amobile user equipment, comprising: a first receiver for receivinginformation signals from entities of a positioning system for use inlocation determinations by the mobile user equipment; a second receiverfor receiving signals from a station of a communication system; andlocation determination means for determining the location of the mobileuser equipment based on signals from the entities of the positionsystem, assistance data signal received from the station, saidassistance data comprising information about the timing of thepositioning system, and a computed difference between the time oftransmission of said assistance data signal from the station and thetime of reception of said assistance data signal at the mobile userequipment, said difference being computed based on an estimated likelylocation of the mobile user equipment relative to the base station.